In recent years, liquid crystal display apparatus have been widely used in displays of mobile phones, personal digital assistants (PDAs), etc. These liquid crystal display apparatus employ a backlight unit that applies illuminating light to a liquid crystal display panel (LCD) from the back thereof. Japanese Patent Application Publication No. 2004-117606, for example, discloses a backlight unit having a light-emitting diode (LED) light source and a lightguide plate that receives light emitted from the LED light source through a part of its peripheral edge surface. The lightguide plate diffuses the received light therein and emits it from the upper surface thereof. The backlight unit further has a reflecting sheet disposed underneath the lightguide plate to reflect light leaking from the lightguide plate back thereinto.
Japanese Patent Application Publication No. 2006-228588 proposes a planar lighting device including an LED light source having a substrate, an LED element mounted on the substrate, and a light-transmitting resin member that seals the LED element. The resin member has a semispherical shape projecting outward along an axis of light from the LED element. The planar lighting device further includes a lightguide plate having a light entrance surface provided with a recess into which the projection of the transparent resin member is fitted. The planar lighting device allows light from the LED element to enter the lightguide plate efficiently through the projection and the recess.
The invention disclosed in Japanese Patent Application Publication No. 2006-228588, however, has difficulty in accurately aligning the LED element mounted on the substrate and the semispherical-shaped resin member, which seals the LED element. Therefore, even if the semispherical-shaped resin member is satisfactorily fitted in the recess provided in the lightguide plate, the lightguide plate may be unable to appropriately receive light from the LED element, resulting in such problems as a reduction in luminance at the light exit surface of the backlight unit concerned and a degradation in the uniformity of luminance.